Means for truing mandrels



March 16, 1937. SUNNEN y y 2,074,061A

MEANS FOR TRUING MANDRLS Filed July @8, 1934 JOSEPH .SUA/Naw.

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MEANS Foa TRUING MANDRELS` y Joseph Sunnen, Kirkwood, Mo.

. j'-Application July 28, 1934, Serial-Nc. 737,365 Y l, y., l, ZIClaims. ,"VMy'` inventionhas relation to improvements in 4methods ofand means 'for truing the mandrels of machines for 'grinding Vpin'holes and it consists in the vnovel features'more fully set forth in the 5 specification afnfd poitedffout in the claims.

fWljiefn themardre'ls of grinding" machines, such shown inyi'fpatentfivo; 1,913,689, dated June 13 1 l P. and `my pending" application SerialA No. 655539`-2gfiled Vunder date of February 6, 1933,

f have been put to considerable use, both the abrasive element and the guide elements of the mandrel naturally undergo wear, such that the surfaces of the elements that contact with the `work are no longer true in the sense that all 15 points along a given line lengthwise of each element lie in a common plane.y Due to the .movement of the work back and forth over the mandrel the elements in time develop high and low points which if permitted to remain interfere with the grinding ofa true'hole. It, therefore, becomes necessary from time to time to correct these irregularities of wear and again restore the mandrel to perfect con-dition. This perfect condition requires that the surfaces of the stone and guide elements that are to Contact with the work must not only be rectilinear from end to end thereof, but should also be longitudinally parallel and transversely curved along the circumference of a common circle. In other words, these contacting surfaces should lie on the surface of a common cylinder.

It is the object of the present invention to provide a method of truing a pin hole grinder mandrel to accomplish the above requirements and also the means whereby said method is practiced. This object and the manner of accomplishing the same will be better apparent from a detailed description of the same in connection with the accompanying drawing, in

which:

Figure l represents a grinding machine embodying a mandrel of the type set forth in the patent and application aforesaid with the truing means applied to said mandrel; Fig. 2 is a perspective view of the truing means herein designated as a truing sleeve; and Fig. 3 is a crosssection through the mandrel and truing sleeve applied thereto, said section being taken on the line 3-3 of Fig. 1.

Referring to the drawing, G represents a grinding machine embodying a driving ,spindle S in which is secured the mandrel M to which the work (not shown) is applied. As above stated, from time to time the grinding stone or abrasive element l and the guide Velements 2, 2 of the mandrel have to be trued or restored to per- `feet condition toieliminate the irregularities of wear. YFor this purpose, I have provided a cylindricalsleeve 3 (preferably of cast iron) of substantial thickness, the inner `surface 4 ofin \which being truly Vct'flindrical and of an initial diameter slightly morethan-the diameter of av circle in ,which thecontacting surfaces of the felem'ents land 2 rotate when adjusted to their innermost position, or for application to the smallest size of hole for which the mandrel is designed.

The sleeve 3 is of substantial thickness so that it may have a long life in view of the fact that its inner surface is gradually worn away by the abrasive contact with the elements l and 2. A slot 5 is provided in the wall of the sleeve 3, said slot extending substantially the entire length of the sleeve (as shown in Fig. 2) and somewhat around the circumference thereof so as to follow the path of a helix. The pitch of the 'helix is not critical but need be just sufficient to produce a shearing effect between the leading edges of the elements and the rear edge of the slot with respect to: their relative rotation when the sleeve is applied to the mandrel for the purpose of truing the same. The slot 5 further serves as a discharge opening through which the particles of the grinding stone l and guide elements 2, 2 liberated from these elements during the abrading action are discharged from the cylinder.

In the practice of my truing method and operation of the sleeve 3, the latter is applied to the mandrel M and the mandrel then caused to rotate in the same manner as when it is used for grinding the pin hole in a piston or other piece of machinery. As the mandrel rotates the operator grasps the sleeve 3 firmly and slowly reciprocates the same from end to end of guide elements l and 2 of the mandrel. During the rotation of the mandrel and the reciprocation of the sleeve 3 the grinding stone l is advanced in the same manner as when the mandrel is applied for the purpose of regrinding a piston pin hole. In other words, the action of the mandrel M is the same with respect to the sleeve 3 as it is with respect to a piece of work, the pin hole of which is being trued.

During this action, owing to the length of the sleeve 3, which is somewhat greater than onehalf the length of the mandrel elements l and 2, the high places (or points of greatest diameter across the mandrel) will first contact 'with the sleeve 3 and be worn down. Said lines of contact between the elements I and 2 and the sleeve 3 gradually lengthen until contact is made between said elements and the sleeve throughout the entire length of the sleeve. Owing to the length of the sleeve it is not possible for the same to be rocked on the mandrel M, but it will be moved backward and forward in parallelism with the rotation axis of said mandrel. Thus, after the truing operation has continued for a suiiicient length of time the contacting surfaces of the grinding stone I and guide elements 2, will have been ground to truly cylindrical form, corresponding with the inner surface 4 of the sleeve 3. As the abrading action between the sleeve 3 and elements I and 2 proceeds the particles liberated from said elements by this action will be continually discharged through the slot 5 so that they cannot work around within the sleeve 3 and score the elements I and 2. The direction of rotation of the mandrel during the truing action is the same as when the mandrel vis used for grinding piston pin holes, as indicated by the arrows in Figs. l and 3. When the mandrel M is rotated in the direction of the arrow (Fig. 3) the edge a. is the leading edge of the grinding stone I and the edges b, b are the leading edges of the guide elements 2, 2. Obviously, these edges travel toward the edge c of the slot 5 and if said slot were disposed parallel to the longitudinal axis of the sleeve 3 the edge c would impinge against the entire length of the edges a and b at the same time and momentarily stick together so that pieces would be broken from the guide elements when the contacting edges again freed themselves. It is to avoid this objectionable result that the slot 5 is inclined, as shown in Fig. 2.

Having described my invention, I claim:

1. In grinding machines having a grinding mandrel composed of a longitudinally extending abrading element and longitudinally extending guide elements, the combination of a truing sleeve having a longitudinally extending slot thru the wall thereof, the edge between one wall of the slot and the inner surface of the sleeve forming a dressing edge for the abrading element when the abrading element is rotated within the sleeve in contact with the walls thereof.

2. In grinding machines having a grinding mandrel composed of a longitudinally extending abrading element and longitudinally extending guide elements, the combination of a. truing sleeve having a helically disposed slot thru the wall thereof, the edge between one wall of the slot and the inner surface oi' the sleeve forming a dressing edge for the abrading element when the abrading element is rotated within the sleeve in contact with the walls thereof.

JOSEPH BUNNEN. 

